Option 1: playing with numbers and decimals

const countDecimals = value => {
  let text = value.toString()
  if (text.indexOf('e-') > -1) {
    let [base, trail] = text.split('e-')
    let deg = parseInt(trail, 10)
    return deg - 1
  }

  if (Math.floor(value) !== value) return value.toString().split(".")[1].length - 1 || 0

  return 0
}
const round = number => Math.round(number * Math.pow(10, countDecimals(number - 1))) / Math.pow(10, countDecimals(number - 1))

Option 2: playing with strings

let round = number => {
  let str = (number).toString()
  let [num, dec] = str.split(".")
  let leading_zeros = ""
  for (const char of dec) {
    if (char !== '0') break
    leading_zeros += '0'
  }
  dec = Math.round(parseFloat(dec.substring(0, dec.length - 1) + "." + dec[dec.length - 1])).toString()
  return parseFloat(num + "." + leading_zeros + dec)
}

Maybe you could use string based solution

Convert a decimal number to string, then split it by the .. Then take a decimal part length substracted by 1, and use it in toFixed on the original number.

You will probably need some additional checks, to see if there is a decimal part of a number

const decimal = 1003.0090270812437;
const text = decimal.toString().split('.')[1];

console.log(decimal.toFixed(text.length - 1)); // 1003.009027081244 

const result = Number((1000/0.997).toPrecision(16))

const result = Number((1000 / 0.997).toPrecision(16))
console.log(result)